From my perspective, it depends on the gender and genes. But I also think the "for life" is a hard talk. If you and the fish are lucky, we are talking 25-30 years. I, for one, don't know what will happen with me in 5 years.
The biggest RTC raised in captivity is an Aquarium in the Netherlands is 5'4" brought in the country in 1972 at around one foot length. There is another one in there only a bit smaller, same age.
On the other hand all my supposed males (6-7) haven't exceeded 2.5' and are 5-6 years old.